Effectiveness of Biochar Amendment on Soil Surface Roughness Variations.

Effectiveness of biochar amendment on soil surface roughness variations Ataallah Khademalrasoul1, Nikolaus.J. Kuhn2, Yaxian Hu2, Bo V. Iversen1, and Goswin Heckrath1 ABSTRACT Soil surface roughness variations play a decisive role in soil erodibility. Soil amending with organic materials has a positive effect on the formation of stable soil aggregates which affect soil surface roughness variations. Recently biochar has been used as an organic amendment to improve the general soil quality. In this study, an experimental field was established on an arable sandy loam soil (Typic Hapludalf). The field experiment comprised of eight plots of 6 m × 8 m arranged next to each other in one row. Four plots were untreated control plots while four other received 2 kg biochar m-2 in 2011. On each plot, a composite sample of approximately 65 kg soil was collected from the topsoil (0-0.20 m) for runoff experiments and soil analyses by bulking soil from six randomly selected sampling points. In a rainfall simulation study under controlled laboratory conditions, the gradual development of crusts as indices of soil surface variations together with surface random roughness was investigated. In this simulation the rainfall intensity was 30 mm h-1 for 3.5 hour. During the simulation event, runoff and sediment were sampled in intervals of 30 min, which in most cases produced enough runoff and sediment in order to measure runoff and erosion from the flumes. Twenty-centimeter transects from the outside rim to the center of the flume were scanned stepwise at a 1 mm resolution using a laser scanner to characterize the microtopography of soil before and after rainfall simulation. Digital surface models were analyzed using variogram models. The soil organic carbon, aggregate stability and particle size distribution of soil and sediments was measured. The results demonstrated the difference of surface variations between biochar-amended and unamended control soils since the biochar lumps were able to alter the soil surface roughness. Also our results showed that the particle size distribution of biochar had an effect on the surface roughness variations. This increase in surface roughness in the biochar-amended soils decreased the runoff and erosion rates. On average, the biochar treatments had cumulatively 27.0% less runoff and 42.5% less erosion compared to unamended control soils. The results indicated that biochar application already in the short-term can lead to an improvement of soil aggregation thereby enhancing the aggregate stability and surface roughness leading to a lowering of soil erosion and runoff. Keywords: Random roughness, digital surface models, laser scanner, rainfall simulator, biochar